This project comprises an invstigation of the structure and functioning of the sodium pump. Rapid quenching studies have shown the presence of an "intermediate" component of the dephosphorylation rate curve in the membrane-bound enzyme from Electophorus electric organ. We have developed two different preparations of soluble Na,K-ATPase. One of these preserves the membrane-type dephosphorylation kinetics, whereas the other type displays monophasic dephosphorylation. Disappearance of the intermediate rate component is correlatd with a doubling of catalytic activity. Since molecular seiving and cross-linking studies indicate that both preparations consist of monodisperse associations of 3-4 enzyme protomers, the provisional hypothesis for current studies is that the native enzyme exists as an oligomer and that modification of oligomeric interactions by the solubilizing detergent is responsible for the altered kinetics. Other studies to correlate these differences with physical and other biochemical parameters of the Na,K-ATPase and to determine the transport competence of the two forms are in progress.